Mickey (the Ferret) has a web site that has pictures and directions on it.
A piece of leather 3/4 of an inch wide by 2 3/4 long will do the trick. Cut the top end to the shape you want, (pointed, etc.) measure down 3/4 fold out, measure out 5/8 and fold again, that is the top of the shelf, fold the bottom of the shelf under, and the remaining piece down. Hopefully this helps?